I love the Oath of the Sea from the new Pantheon book, but it appears to have one major oversight. Specifically, most Paladin Oaths gain a new ability at 7th level, but Oath of the Sea doesn't--it skips directly from the 3rd-level ability to the 15th.

Endless BreathStarting at 7th level, you and friendly creatures within 10 feet of you cannot be subject to suffocation while you are conscious. In addition, you and your allies have advantage to resist breathable poisons and magical effects that manifest as clouds or rely on being breathed. Clouds, fogs, and similar effects still provide cover, and obscure sight as normal.

You may want to explicitly add in the "Waterbreathing" thing, or some sort of equivalent phrasing; I could totally see some rules-lawyer GMs insisting that "No, you can't suffocate--but you'd be surprised at how much damage you can take before you die."

Just an example, sorry. (And I think it did inflict damage in previous editions?)

And, yes, it should work in any situation, but I could still see this effect being super traumatic in certain situations--yes, you can't suffocate in the depths of space, but neither can you breathe. Big Trouble In Little China.

I think it would be nice to adjust the effect a little. Like:

"Starting at 7th level, you and friendly creatures within 10 feet of you can breathe comfortably in any situation, even when air is unavailable or otherwise hazardous. Creatures under this effect cannot be subject to suffocation while you are conscious..."

If you feel really strongly about the original phrasing, though, I'll get off my soap box.